engine over-revving when on idle with A/C on

[TrexMex]

Hello,

When idling (e.g stopped at a red light), the engine idles at ~1100 RPMs if the A/C is turned on; If I turn off the A/C and flip it back on immediately, the engine will go to ~600 - 700 RPMs and stay there without any problems. This seems to come and go but it happens most of the time.


Help?

 

[sparky]

Mine does that sometimes too, not sure what it is, when i turn my a/c off it still idles high. but it seems i have read that if the engine is running a little hotter than normal the computer will idle it faster to try and cool it back down. I may be way off, maybe someone else will chime in and help.

 

[evanesce69]

auto or manual???

 

[sonicboom919]

clean your maf sensor

 

[TrexMex]

clean your maf sensor

Just cleaned it, along with the throttle body, new spark plugs (Motorcrafts), and timing adj. as part of a full tune-up. It actually started over-revving after all this. Besides this problem the truck is running much better now (was lacking a LOT of power). I also Sea-Foamed it (Gas tank - Booster Vacuum Line - Oil) and for what is worth, the thing worked its magic, It almost seems like I'm driving a new truck if you don't pay attention to all the exhaust leaks, lol.

One other thing that makes sense is that 'round here it gets VERY hot, so the computer adjusting to that might be a cause. Then again, 1100 RPMs seems a little bit over what I would expect. last week was specially hot (110s avg), and it's my first summer with the truck in this weather, so I'm still getting used to how it performs.

auto or manual???

Manual, 5spd.

 

[evanesce69]

my 3.0L sometimes surges at idle with air on. It is also a 5 speed.

Did you reset the computer when changing/cleaning the parts? Disconnecting the negative power lead while doing the service should do the trick. If not, the cpu may be trying to use the old "dirty" information with the new/clean parts. If you didn't, not to worry though, it will eventually flush out the old information. It just may take a while.

This "limbo" may explain your current surging.

 

[TrexMex]

Did you reset the computer when changing/cleaning the parts? Disconnecting the negative power lead while doing the service should do the trick. If not, the cpu may be trying to use the old "dirty" information with the new/clean parts. If you didn't, not to worry though, it will eventually flush out the old information. It just may take a while.

This "limbo" may explain your current surging.

I did disconnect the battery when I performed the tune up, but I guess not long enough. I was giving the engine a good wash last sunday and removed the battery to avoid any short circuit for about 2 hours, and it hasn't misbehaved since then. So I probably fixed my problem by accident!!! You usually CAUSE problems by accident, but worked the other way around this time, for a change LOL.

Thanks for the good advice y'all!!